Database Competency 4.1

A(n) ________ trap occurs when a relationship is improperly or incompletely identified and, therefore, is represented in a way that is not consistent with the real world. design key relationship entity

design

A specialization hierarchy provides the means to define a special supertype attribute known as the subtype ________. separator identifier typer discriminator

discriminator

What is another name for the extended entity relationship model? enhanced entity relationship model redesigned entity relationship model Chen model complete entity relationship model

enhanced entity relationship model

In modeling terms, the ________ contains the common characteristics and the entity subtypes contain the unique characteristics of each entity subtype. superentity entity supertype base entity higher entity

entity supertype

What is the default comparison condition for the subtype discriminator attribute? equal to greater than or equal to greater than less than

equal to

A supertype contains those attributes that are ________ all of its subtypes. common to inherited from foreign keys in different from

foreign keys in

What is the purpose of an entity cluster? improve readability of the ERD define physical database storage for related entities make the ERD more complex group related entities into a single table

improve readability of the ERD

When defining a 1:1 relationship where one side of the relationship is mandatory and one is optional, where should the foreign key be placed? in the table that defines the mandatory entity in the supertype in the table that defines the optional entity in the subtype

in the table that defines the optional entity

The property of ________ enables an entity subtype to inherit the attributes and relationships of the supertype. inheritance generalization uniqueness specialization

inheritance

In specialization hierarchies with multiple levels of supertype/subtypes, a lower-level subtype ________. inherits all of the attributes and relationships from its direct supertype only does not inherit any attributes or relationships inherits all of the attributes and relationships from all of its upper-level supertypes only inherits attributes and relationships from the top-level supertype

inherits all of the attributes and relationships from all of its upper-level supertypes

A ________ is a real-world, generally accepted identifier used to distinguish real-world objects. candidate key natural key specializor discriminator

natural key

In a data model, grouping employees into types avoids unnecessary ________ in the employee attributes. data anomalies data redundancy relationships nulls

nulls

What is the best data type for a primary key? text numeric boolean date

numeric

Arguably, the most important characteristic of an entity is its ________. relationships primary key attributes name

primary key

The ________'s function is to guarantee entity integrity. primary key index discriminator entity name

primary key

One important inheritance characteristic is that all entity subtypes inherit their ________ from their supertype. foreign keys indexes primary key attribute candidate keys

primary key attribute

Entity supertypes and subtypes are organized in a(n) ________ hierarchy. entity generalization specialization super

specialization

In an aviation company's data model, a PILOT entity might be a(n) ________ of the EMPLOYEE entity. subtype cluster supertype attribute

subtype

A(n) ________ is the attribute in the supertype entity that determines to which entity subtype each supertype occurrence is related. inheritance key supertype selector subtype entity subtype discriminator

subtype discriminator

The implementation of disjoint subtypes is based on the value of the subtype discriminator attribute in the ________. primary key attribute supertype subtype foreign key attribute

supertype

________ relationships occur when there are multiple relationship paths between related entities. Joined Shared Redundant Nonkey

Redundant

________ is the top-down process of identifying lower-level, more specific entity subtypes from a higher-level entity supertype. Specialization Overlapping Completeness Generalization

Specialization

________ primary keys are especially helpful when there is no natural key. Surrogate Composite Null Shared

Surrogate

________ data refer to data whose values change over time and for which you must keep a history of the data changes. Time-variant Historical Closed Time-complete

Time-variant

A weak entity in a strong identifying relationship with a parent entity is normally used to represent ________. a real-world object that is existent independent of another real-world object a real-world object that is represented in the data model as two separate entities in a weak identifying relationship two entities related by a weak relationship a real-world object that is represented in the data model as two separate entities in a strong identifying relationship

a real-world object that is represented in the data model as two separate entities in a strong identifying relationship

What type of primary key should be used as an identifier of a composite entity? single attribute foreign key composite key surrogate key

composite key

A(n) ________ trap occurs when you have one entity in two 1:M relationships to other entities, thus producing an association among the other entities that is not expressed in the model. entity key fan relationship

fan

In addition to the normal behavior, the EER model also supports specialization ________ where a subtype can have multiple parents (supertypes). lattices webs networks nets

lattices

What is the ideal number of attributes used to make up a primary key? 1 2 3 or more there is no ideal number

1

A specialization hierarchy reflects the ________ relationship between EMPLOYEE and its subtypes.

1:1

At the implementation level, the supertype and its subtype(s) depicted in the specialization hierarchy maintain a ________ relationship. 0:1 1:1 1:M M:N

1:1 (see page 155)

In MS Visio, you select the subtype discriminator when creating a category using the ________ shape from the available shapes. Entity Category Item Inheritance

Category

_______ subtypes are subtypes that contain a unique subset of the supertype entity set. Disjoint Unconnected Unique Exclusive

Disjoint

________ is the bottom-up process of identifying a higher-level, more generic entity supertypes from lower-level entity subtypes. Specialization Generalization Completeness Discrimination

Generalization

The relationships depicted within the specialization hierarchy are sometimes described in terms of "____-A" relationships. HAS IS NOT WAS

IS

________ subtypes are subtypes that contain nonunique subsets of the supertype entity set. Joined Shared Complex Overlapping

Overlapping

Every subtype can have ________ supertype to which it is directly related. zero or more only one at least one more than one

at least one

It is common to avoid the display of ________ in an ERD that uses entity clusters. relationships cardinality attributes entity names

attributes

What is another name for a subtype? parent entity base entity child entity subentity

child entity

An entity ________ is a "virtual" entity type used to represent multiple entities and relationships in the ERD. section cluster group segment

cluster

The EER model builds on ER concepts and adds support for entity supertypes, subtypes, and entity ________. extension housing joining clustering

clustering

The ________ constraint specifies whether each entity supertype occurrence must also be a member of at least one subtype. uniqueness specialization completeness inheritance

completeness